Welsh Water Llanberis Caisson Humus Settlement Tank


Due to site constraints at Welsh Water’s Llanberis waste water treatment site, a proposed replacement of a Humus Settlement Tank (HST) was required to be constructed below existing ground levels.

Initially, we were engaged to provide a design service for the caisson so Welsh Water could construct their tank. However, the scope of the task changed when it was decided that the caisson design, and design of the HST tank, could not be separated.


Our Tadcaster team, consisting of structural and geotechnical engineers, collaborated with Mott MacDonald Bentley and subcontractor AE Yates. Together, we provided a well-rounded service for Welsh Water and the caisson HST tanks including design of all the ductile iron pipework. The project team was led by David Gwede and comprised of Phil Bentley, Henry Shone and Ellie Cowell.

Thanks to stellar work from the team we delivered a detailed geotechnical, structural and mechanical design which was received well by Welsh Water. As a result of our success with this project, we are now the sole supplier for AE Yates design where they need statutory approval.


We promoted collaboration and interaction between our design team, Welsh Water, Mott MacDonald Bentley and AE Yates. The collaborative approach meant the solution provided was cost effective and delivered four weeks ahead of schedule.

Want to know more?

For more information on this project contact David Gwede, Technical Director. You can also find out more on our geotechnical web pages.

We focus on managing and controlling water and the impact water has on client’s assets and infrastructure. Wherever difficult ground conditions, sensitive environments or ambitious projects present geotechnical challenges, we provide robust and advanced solutions that are tailored to meet clients’ specific requirements. We have a growing portfolio of shafts and tunnels work and will soon be able to deliver on significant tunnelling projects.

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